text:
How does a full fuselage and structure inspection happen in practice ? (for modern Civil airliners)
What are the intervals at which a full structure inspection take place ?
How much time does a test commonly take for narrow and wide body aircraft ?
Is every part in the structure manually inspected by the operator in level C Check or some parts only depending on the Structure repair manual (SRM) of the aircraft?

Such elements are generally dependent on the certification authority, and can vary from country to country. Which country are you targeting?

What do you mean by a "full fuselage and structure testing"? This can be anything from the manufacturer's initial structural testing ("proof test"), which usually only happens once on a prototype designates for that purpose which is cycled until it fails) to the fatigue inspections performed during the airframe's service life (which are typically dictated by manufacturers)

i didn't put that in perspective !! lets say im targeting UAE !

the second one, during the airframe's service life

There is a great video of a full D-Check for a 747 here

The FAA "Class D" maintenance/inspection of commercial airliners, which must occur every 6 years, is extremely thorough:

The cabin trim is completely removed to inspect the airliner's skin and superstructure from the inside. Seats, safety equipment and control system linkages are also inspected in detail with each individual cable or wire tested.
The plane's exterior paint is removed to inspect the exterior skin, including rivets and seams.
All critical moving parts on the exterior of the plane (engines, gear, ailerons, flaps, spoilers, rudder, elevators, shock booms, etc), are removed from the plane, disassembled and visually inspected for wear or damage, then re-assembled and tested.
All pressurized lines (hydraulic, water, fuel) are removed from the plane and each part individually visually inspected before being re-assembled and pressure-tested in the plane.
The cockpit is stripped, all moving parts in the control column and throttle assemblies visually inspected, and all flight instruments visually inspected and tested.

There are many more maintenance/inspection tasks than I list, I'm just going through the major ones. The plane is more or less stripped to its bare metal frame, every component visually inspected and tested, then the aircraft is reassembled with individual systems tested again on the airframe. The process can take up to two months for each aircraft, and can cost between 5 and 7 million US dollars. Most major airlines have either their own in-house maintenance crews or the manufacturer perform this maintenance, with a team of FAA-employed inspectors overseeing and signing off on all the work.
Most airliners receive 3 Class D inspections in their lifetime; at the fourth, occurring around 24 years of airframe age, the cost of a Class D is typically not considered worth it given the aircraft's remaining value, and the aircraft is usually retired and either sold to smaller non-US airlines operating in jurisdictions with less stringent standards, mothballed and stored for potential replacement parts value to the rest of the fleet, or sold for scrap. Some airframes in service with some airlines have been kept through four Class Ds in order for the airline to have sufficient time to procure replacements; American's remaining MD-80s are largely newer airframes acquired in the TWA merger, but there are a few of American's own deliveries left in the fleet which are past 24 years and are still around mainly to allow American sufficient time to work through the bankruptcy, United merger and procurement of replacements (Boeing's 737 production lines are going full-tilt and American is not the highest-priority customer, so American had to split its order in this class between the 737 and Airbus's A319 and A321).
Because of the level of detail and deconstruction required, including complete cabin trim and paint removal, airlines often use this maintenance interval to perform any desired upgrades or tweaks to their fleet configuration. Common upgrades in recent years have included:

adding winglets for vortex reduction (reducing drag and allowing closer spacing at busy airports),
upgrading avionics and even control systems (some older airframes can be upgraded from direct cable-driven hydraulics to electro-hydraulic controls allowing partial automation of flight with EFDs),
upgrades to cabin trim including re-spacing of passenger seats (more or less legroom or "slant", balancing between class seating),
replacing galley equipment and other secondary systems that may be a different standard from the rest of the fleet,
adding new passenger conveniences (such as satellite-based Wi-Fi, headrest IFE, etc) and
new exterior paint schemes for corporate rebranding (such as American's ongoing rebadging from their decades-old AA silver to the new American white, and Southwest's recent move to the "Heart" scheme from its older "Canyon Blue" and the original red/gold before that).

Aircraft acquired in airline mergers are often the highest priority as the airline seeks to rebadge and standardize the acquired fleet to operate alongside its existing planes (and ensure no corners were cut by a struggling airline that would create liabilities going forward).

thanks for the detailed answer, there are more issues i would like to know about since you seem expert on the subject.
1-regarding aircraft exterior skin (different types of composites) how often do they need to be checked (without dis-assembly) using conventional methods like (ultrasonic and active thermal imaging) for all structure faults (like delamination, disbonding, cracks, weak bonds or rivets  ... etc)  how much does it cost to inspect in terms of money and working hours ?
thanks again :)

A comprehensive visual inspection of the airframe's exterior skin is done at every "A-check" which is performed about every 250 flight hours and can be done overnight. Inspection of the most likely places to show stress (wing-body joint, engine nacelle mount, on/around control surfaces etc) is done at least daily if not between flights. All higher levels of maintenance include items checked in these two levels, much like your car's 30k service interval typically includes an oil change and tire rotation/inspection. More in-depth inspections are performed at C-check intervals.

do u have more information about what i exactly the type of structure inspection (airframe, composite structures) in B and C checks regarding type, time, and labor cost ?
truly thankful :)

No I do not; exactly what is done at every tier of maintenance interval, and exactly what those time intervals are and thus what it costs to maintain a particular aircraft, depends on the model of aircraft. Additionally, airlines are allowed to stretch out the inspections normally performed in one tier across several other maintenance stops, which is called "progressive maintenance" and keeps the aircraft closer to a serviceable state at any given time in its life.

The inspection schedule of each aircraft is decide by the manufacturer in coordination with the regulatory authorities and released to the customer and varies from aircraft to aircraft.

In case of civil aircraft, 'full' inspection, usually called the D-level checks, is carried out every 4-5 years.
It depends on the aircraft condition and factors like aircraft age, how it was maintained etc. it is time consuming, usually taking a few months depending on the replacement requirements and resources (like no. of technicians available).
The structure is thoroughly inspected- Every single part is subjected to checks in addition to any checks mandated by regulatory authorities/manufacturer or required by customer.

Aren't most airliners on a progressive inspection now rather than putting the aircraft down for such a long period of time?

@Lnafziger - As I understand it, there's so much to be done on a major airliner for a Class D that just doing it all at once is the most efficient way; the total time out of service involved in doing all the Class D inspections over more smaller maintenance stops would be greater than just biting the bullet. At the very least, no lesser level of maintenance involves stripping the cabin trim and exterior paint for a full fuselage stress inspection which by itself would be a lengthy and costly process.

However, you seem to be right that smaller, more frequent inspections incorporating a rotating schedule of D-check items are the norm especially for VLAs (of which there tend to be few airframes in service and fewer spares capable of running the route). The first D-check of an A380, however, was a complete all-in-one teardown, so it varies by model, airline and airframe age.


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What is the take off and landing performance of the MQ-9?
At maximum takeoff weight (listed on wikipedia as 10,494 lb (4,760 kg), 11,700 pounds (5,300 kg) with upgraded landing gear), what is the minimum runway distance required (not including safety margin) for an MQ-9 takeoff at sea level on a standard day?
It is also stated (same reference), that the improved landing gear provides a 30% improvement in landing max weight.  What is the landing max weight and the corresponding minimum runway distance (again, without safety margin and on a sea level standard day)?

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What instructions should I give to an untrained passenger for Hand propping Cessna 172N as a pilot?
Does anybody know what is the most effective way of hand propping a Cessna 172N, with a passenger who is not mechanically inclined.
So you need to give them the most easy to follow and simple instructions. Like after pulling the hand brake, and priming and opening the throttle 1/4 inch what do you tell them to do?
I would push the throttle gently in after I'd hear the engine coughing to power when hand propped, while keeping my feet on the brakes, till  engine's smooth revving and maintaining power.
But to a person that has no familiarity with the noise of the engine and does not know what to expect, what should I say.
Edit
I thought I should elaborate a bit to shed some light on what happened.
We had come back from a half a day of  hiking around the hills of Santa Ynez in the afternoon with my hiker friend. After trying to crank the ignition a couple of times, it just moaned jerking half way through a hesitant arc.
We looked around for something to use as chocks, found two rocks like 8-10inched and kind of heavy and pushed them to a locking position in front of the tires.
I set the throttle; told him not to touch it before I jump back after cranking and wave him all clear. Then he pushes the throttle by half an inch while pushing the breaks. We brought the engine back to life after a few tries.
After I felt we have a enough of prop rotation inertia I got on to the right seat and brought the RPM down. He got out and removed the rocks. Got back in and we flew back to Van Nuys.

You should say you aren't going flying that day and get the starter fixed.

I'm pretty sure hand propping is illegal if the other person in the plane is not also a fully-qualified pilot in my country (Germany). You definitely want to check legal requirements as well.

To add to legal requirements, all original equipment should be working, or deactivated/disconnected and placarded inop.  IDK if you can legally do this to a starter, but assuming you can, get a mechanic to double check the starter isn't engaged or loose, or remove it completely - I've seen a 182 nearly catch fire inflight when a partially bad starter began shredding gears.  All that said, do what you want, but if your untrained passenger screws up and the plane goes into a building and/or hurts people, you are gonna have to explain it to the FAA, the insurance company, and maybe a civil court.

@GdD: A reasonable answer if you happen to be at a field where there's a mechanic (or you have the necessary tools &c).  Not so reasonable if you happen to be on a dirt strip a long ways from anywhere.  (Been there, had to do that :-))

The person at the controls MUST know how to handle potential engine starting emergencies such as an engine fire. They MUST know how to shut off fuel and batteries.

Was that "non-intuned" or "non-entombed"?  I don't think "intuned" is a real word, but I suspect one or more of the parties involved will soon be "entombed".

Related

How about having the less qualified person on the muscle job instead of the brain job?

@kamran you got away with it but you were taking a huge risk.   That's all I can say.  What if he pushed too far and then went into panic mode.  In panic mode, a person just does the same wrong thing harder and harder.  An engine at full or close to full power will easily jump chocks and push rocks out of the way.   Go out and by some line, good for 500 lbs test (that's about the static thrust of a 172 at WOT), and carry that around with your flight kit.

@kamran also, when you were swinging the prop, did you have the mags on BOTH?

Umm, DO NOT DO THIS?  You’re asking for an accident here.

That is crazy.  DON'T just rely on an person who's new to airplanes and only training is 5 minutes of showing them what to do, who may or may not react correctly when it springs to life, as the only thing preventing the plane from heading off somewhere while you try to dive clear.  Don't. Do. It.
Tie the tail. To something.  Anything.  Use the passenger and show them what to do and give them a careful briefing, but tie the tail down anyway.  You don't know how the passenger is going to react if things go off kilter.  And if tying the tail is simply not an option, and you have no choice because you have to leave because zombies are approaching, at least point the airplane toward some obstacle just beyond the normal turning radius, like a wire fence, for it to run into when it takes off with your passenger confused and frightened because they pushed the throttle in too much and let off the brakes when the thing jerked forward on them, with you diving for your life.
Once it's running at idle and everything is kosher, set the parking brake and you can walk back to untie it with your passenger ready to switch the ignition off if it starts to roll away.
And make sure to use the correct terminology with your assistant.  Don't say "switch on/switch off".  It's "Switch off" for ignition off, and "Contact" for ignition on (it's old fashioned sounding, but it works).
I have been personally burned by a guy who did things the usual way, when I said "switch off", then repeated "switch off" to make sure he heard it.  He thought I'd said "Switch off" then "Switch on" when I'd just said switch off twice.  I neglected to brief him on the use of the word "contact" so it was my fault in the end.  Anyway, I got a nice noisy surprise when I turned the prop over thinking ignition was off.
Hand propping is quite a dangerous operation, especially on tri-gear airplanes where you have to lean forward to do it.  I trust you yourself have been properly trained, and know things like not to hook your fingers over the blade so you don't get pulled into it if it kicks back, that sort of thing.

This is good advice, I would point out I haven't seen a Cessna with a working parking brake in 15 years of flying.

+1 for leading out of the gate with that is crazy. I'd give a second +1 if I could for the zombies.

Yep it's one of those topics where bluntness is necessary, although it's not meant to be insulting or demeaning. I have acquaintences today that own a, you guessed it, an Aeronca Champ with an A-65 engine in a partnership, and they start it routinely with nobody aboard and using only little metal chocks.  I've told them it's crazy also.

@John K How do you intend to pull the blade without hooking your fingers over it?

You place just the tips of your fingers over the edge of the blade, about the middle area of your fingerprint, not at the joint where you would normally do it by instinct.  The little notch in the finger joint makes a great hook and increases the ability of the blade to pull you in if it kicks back.

Re the "Switch Off" vs "Switch On" confusion we should learn from the sailing community. They use "Readyabout" vs "Prepare to jibe"  and "Hard a lee" vs "Jibe ho". Maybe we need a "Switch On" vs "Turn off"

Too close sounding still.  "Contact" has been used since the beginning of aviation.

@John K Okay, yes - that's the way I've always done it. Didn't think about the 'hook' possibility, it just seemed right. I also had a few very experienced people show me the proper way to do it (stand close, balance to fall away, not forward, swing your entire body, etc.), which has served me well over the years that I've had to prop various airplanes. The best ones for this are glider tow planes - they have a tail hook, which can be released from inside. No danger of a runaway with those. I've also used tiedowns, on wings and tail, then untied them after the engine was safely settled at idle.

I carry around a 50ft line, coiled into a package the size of a submarine sandwich, in the baggage area that I can run from the cockpit, around an object like a fence post or tie down, and back into the cockpit so I can release it while seated and reel it in.  It's still in the wrapper it came in.

I’ll second John K’s answer.   Do not attempt to hand prop an airplane without receiving professional instruction on how to do it safely. It is a real easy way to get seriously injured or killed, as this idiot almost found out.

It should also involve two competently trained people, one to do the hand propping, and the other at the controls of the airplane during the process to control fuel, ignition and throttle throughout.

Back in the 70s, at a little airport north of Toronto, Ontario, a guy was hand starting his Champ unsecured and overprimed it.  He switched off, opened the throttle wide, and flipped it through backwards to clear it out, then switched on the mags and gave it a flip... and off it went, taking off and doing 2 circles of the airport before crashing, amazingly only a couple hundred feet from where it started and cartwheeling into a ball without any other damage or injuries, other than the picnic table. It got a little 2 inch column item in the Toronto Star the next day.

@JohnK This sounds hilarious. Any links to archive articles?

No I tried to find it on the Star web site once but no luck.  The airport was called King City Airport, so see what you can find. The Champ will fly unpiloted because the pilot sits pretty much exactly on the C of G so there is no trim change.  This one went on a climbing left turn that turned into the beginnings of a descending left spiral. There was a Champ in Pennsylvania I believe that did the same thing and flew straight for quite some distance before crashing itself.

The video was disabled on Youtube.

@nomen No it wasn't, it's disabled from playing while embedded in websites other than YouTube.  You can see it by clicking the "Watch this video on YouTube" link that shows when you try to play the video.

If still in doubt, make sure you don't miss the two still pictures. You will find the link in the description of the video on youtube.

If the person operating the throttle has to react within a fraction of a second to a changing sound that's unfamiliar to them, they're doomed.  So play them a few videos of good and bad starts to make the sounds familiar.  Tell them what to do in reaction to the changes.  Quiz them a few times to ensure they understand.
This might take ten minutes, but then they'll be happy to have mastered a new skill, and you'll have gained a second pair of ears listening carefully during the flight itself.

I wish I had the luxury of having data reception. It happened to me last year in Santa Ynez. We had to look for boulders to use as chucks, it was kind of a experience for both of us.

... and if they're overwhelmed by this amount of instruction, you can't count on them to do anything critical.  In fact you probably shouldn't count on someone reacting properly the first time after having only watched videos and talked for a few minutes.  IDK if you've ever played World of Warcraft or other online MMORPG, but the first few attempts at something often have spectacular failures of players to react to something they had watched a video about. If reacting properly is safety-critical, you can't put that in the hands of someone totally inexperienced even if they seem interested

Yep.  That's why I wrote "Quiz them a few times to ensure they understand!"

A c172 is hard to prop safely, most trigear aircraft are. Do not let any non-pilot get near any prop! In an emergency, say your stranded on a Baja desert strip with a dead battery, tie down the tail, work all controls yourself,ie switch's,mixtures,throtles etc. If I think well of my passenger I might place his hand on the throttle to pull back on my signal,and prop it yourself, if you've been trained, If not? activate your ELT and pray for a helicopter.

Most important: tell your untrained passenger to keep the brakes applied no matter what. Then try to push the plane to make sure he's really on the brakes.

You can't verify that he's still on the brakes while you're hand propping.  Use wheel chocks or tie down the tail.

The question was what should you tell the passenger, not what else you should do.

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Why might a moving map Android app consistently record altitude off by 120 feet?
I fly Cessna 172 and Cherokee Warrior both older models without a GPS.
I have a very useful freeware navigation app on my android phone which is really good in every regard other than it always reads my altitude a bit higher than were I am.
Best example is when I am taxiing my track and its projection on the ground which should have merged are separate.
The app does not have any setting for adjusting this! I wonder if there is any explanation for this. The app superimposes my 3d coordinates on a moving sectional chart. I re-installed the app which didn't help.
Here is my flight KML on Google Earth on my approach and landing to Catalina airport last Sunday.

What kind of phone do you have? It could be GPS error, it's less accurate with respect to altitude. If the phone has a barometer, it needs to know sea level pressure just like an altimeter. Also, what app are you using?

I use Blu Vivo5,5 which is kind of no brand, but after talking to fellow pilots I got it. It is 8core and shows no errors whit land navigation apps. The reason I got it is it already came with 64gig memory and I put a micro card in it with 64 more to be able to record videos of my flights.

@foot sorry i skipped this bit, the app is Oruxmaps. It has many features and allows you to set many levels of alerts. Did I say it is free?

Glad you asked this. I've observed that my cell phone, using GPS Status app always shows my elevation exactly 40 ft lower than my Garmin Nuvi in my car. I would chalk it up to the vertical inaccuracy inherent in GPS and the fact that they're both consumer level devices, but it always seems to be exactly 40 feet difference

This question is certainly relevant to aviation, but it's really better suited to android.SE in my opinion, and may already be answered there

@Pondlife I checked the link and seems to be a fair answer. We pilots who use the smart-phone apps are aware of the shortcomings and use them as a back up. But my question is why the error shows consistently the same as if just a calibration away from being correct. Advantages of the app are many, e.g. it tells you how far away you are from the destination or when you have to call-in and report your intention to approach or center. I think we private pilots should take advantage of new, convenient technology. Another feature that I like is track recording, it's a very good learning tool!

I vote to re-open. It is not specific to android, it is specific to the way GPS works with height internally; it uses the WGS84 ellipsoid. This affects many aviation systems including TAWS/ EGPWS, ADS-B, GLS, etc

I also vote to re-open. For aviation, it is important to understand how GPS works, and why different GPS devices can give different results. The fact that the device was an android phone here doesn't matter.

It could also be off due to an incorrect altimeter setting in the aircraft which would cause the aircraft to actually BE at the incorrect altitude.

@Lnafziger I doubt it. I fly with well maintained planes and check the ARROW and we have a squawk book which any pilot detecting issues will mark them. I set the altimeter after receiving ATIS and when I am transitioning between different centers, they give you the numbers and traffic advisory. Also the two track lines magenta and cyan, both are graphed by my app, planes altimeter is not shown here but I notice this when in the app I get premature above ISL glide angle warning when I practice ISL approach.

@kamran I doubt it too, just pointing out that (for some future visitor) this could be a cause of the problem.

While I think it would be unusual in 2016, it is possible that the unit is recording altitude as distance from the ellipsoid rather that distance from geoid (model of MSL on the earth used by the receiver).
If you use this NOAA calculator, you can find the geoid height for a single spot.  At the location you show, it's 37m or 122feet.  That's suspiciously close to the difference you're seeing.
Output from GEOID03
                                         latitude        longitude       N
Station Name                            ddd mm ss.sssss ddd mm ss.sssss  meters
USER LOCATION                            33 24 15.77000 119 24 57.49000  -37.259

If this error is constant over time (multiple recordings), then I think it's more plausible than random error sources.

Good thought, he would have to check different airports to see if it changes.  Also, one flight wouldn't matter because the difference could be due to barometric pressure changes (which really tells me that it shouldn't be a consistent 120' difference over time unless you are able to enter the altimeter setting in the app, which I doubt).

@Lnafziger  i actually will test the GPS readings on three cellphones i have on my next flight from KVNY via KOXR to KSBA. I well compile a chart comparing the plane's altimeter reading to these and see if there is a pattern.  I just need a passenger to keep track of data and mark them on regular intervals.

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Are there studies to find surface treatments to reduce the drag of an airfoil?
I know that by designing an airplane or a car close to a teardrop, we can reduce the drag. My question has to do with the surface friction treatment. Some torpedoes glide in water more efficiently when wrapped in bubble cloaks.
Some feathers have textures to reduce friction. Some modern bathing suits textures help reduce friction.
Are there studies on surface treatments, such as texture, special paint, grooves, or perforations, to reduce drag?
edit
Implied in my question is: If there are any results that do reduce skin friction, where have they been applied?

Literally thousands

@sophit  I think the question -- asked as "are there studies on this?" truly can be answered with what you have here and the slightest bit of elaboration.  Like a sentence or two on a couple of the studies and a link to each, followed by the link you posted supporting the statement "... and thousands more like these." The question is asking, has this been studied, and you provide conclusive proof that yes, in fact it sure has.

@RalphJ: Sorry I don't get your comment. Are you suggesting me to write a proper answer or not?

Related: What surface materials do airplanes use to reduce friction

A lot may depend on Reynolds number, but bubbles around the torpedo may be analogous to boundary layer studies.

@sophit Yes, please do

This seems to be so broad that the only possible answer to the question is "Yes".

Do airplanes fly?

Here's one that I know of:  "There’s a team of researchers at NASA’s Langley Research Center in Virginia who are studying ways to prevent the remains of insect impacts from sticking to the wing of an aircraft in flight .....  testing different coatings to see which do the best job at preventing bug build-up and the resulting disruption of air flow that reduces fuel efficiency." From this document - Nothing Bugs These NASA Aeronautical Researchers

Well, since nobody else is going to answer this... Y'all are welcome. ;)

Yes, there are literally thousands of studies on the subject.  A keyword search on this link brings up many examples.  (credit to Sophit)
There's also a similar question on this site that may be useful.  (credit to Peter Kampf)
And there are surface material studies for other purposes that you might also find interesting.  (credit to Steve Pemberton)

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Shouldn't there be ATIS/sign information on sloped up runways?
I landed on Catalina island runway 22 last Saturday after the installation of a new concrete runway.
To make it easier for heavyweight planes to land and after a short roll stop, they have made the runway curving up. It was very tricky to land. Because of optical illusion.
I realized at the numbers I was barely a few feet up and considering the fact that the runway starts at the edge of a deep cliff, it was potentially catastrophic.
I make sure I watch out for this and adjust my glide slope next time.
My question is shouldn't they provide some sign or on the ASOS add a heads up.
To clarify, the US Marines did the renovation of Catalina project recently which apparently has finished about a week ago. They have changed the topography of runway in a certain way, made it like bowl apparently, to make it easy for heavy airplanes to land in this short runway.
The changes have not been reflected in VFR charts or Supplement, or other aviation documents, at least to the best of my knowledge.
EDIT
I just add my comment for pilots who plan to land at Catalina.
Because of the fact that the vanishing point (the point the sides of the runway merge in horizon in pilot's perspective) has changed, appearing higher than before, at the short final one perceives they are flying at a higher altitude, look out for this.

Re "I realized at the numbers I was barely a few feet up...", isn't that where you're supposed to be?  Unless there's a chance of significant downdrafts at the runway end, in which case I would think there'd be a displaced threshold.

If you familiar with the Catalina airport there is always current pulling you down. Because of the geometry of the island. You want to be 50 feet up minimum.

Where would you put the sign so it can be seen in time for approach setup?

They have  a big hangar visible from miles away the could put it there or erect a sign, or the nice gentleman manning the tower, he is not ATC, he could give you heads up.

It's your responsibility as PIC to be familiar with the airfields you visit, that means research.

@GdD, I did look up "AirNav' and 'SkyVector', nothing! May be its just too soon. I hope my post will be useful for other pilots who want to land there.

Deliberately making a runway go up or down hill is a new one to me.  Sounds more like they extended the runway or a displaced threshold on sloping terrain.

@John K, it used to have a hunch almost 2/3 down from 22 threshold. I am friends kind of with the guys at tower. I asked him over a cup of coffee, he said they curved the hunch up to make it easier for the larger guys..

Airnav says "RWY 04 FINAL 2,300 FT STEEP 2.1% DOWNSLOPE; RWY 22 UPSLOPE PREFERRED LANDING." and "PILOTS CANNOT SEE ACFT ON OPPOSITE ENDS OF RWY DUE TO GRADIENT, MUST ANNC TAKING ACT RWY ON UNICOM PRIOR TO DEP". Which parts did you check?

This is off-topic, but what is the guidance for Tenzing–Hillary Airport (IATA: LUA, ICAO: VNLK) in Lukla, Nepal? This is the craziest airport I have ever landed at or took off from.

@fooot, I have seen that, it is changed now.

I know it is my responsibility to check everything. I think it helps anyone potentially planning on landing there: because of the higher vanishing point of runway in this particular case one falsely perceive they are approaching at a higher altitude at short final.

FAR 91.103 says (emphasis mine):

§ 91.103 Preflight action. Each pilot in command shall, before
  beginning a flight, become familiar with all available information
  concerning that flight. This information must include -
(b) For any flight, runway lengths at airports of intended use, and
  the following takeoff and landing distance information:
(2) For civil aircraft other than those specified in paragraph (b)(1)
  of this section, other reliable information appropriate to the
  aircraft, relating to aircraft performance under expected values of
  airport elevation and runway slope, aircraft gross weight, and wind
  and temperature.

The most "reliable" place to find this information is the FAA Chart Supplement, which says this for KAVX (emphasis mine):

Rwy 04 final 2,300´ steep 2.1% downslope, Rwy 22 upslope preferred
  ldg. Pilots cannot see acft on opposite ends of rwy due to gradient,
  must announce taking acft rwy on unicom prior to dep.

Any time you see mention of runway slope, you should be aware that something strange (and likely dangerous) is going on there.  Ditto for the cliffs on the diagram, which you are expected to know would create a downdraft on short final.
Since you were legally required to become familiar with this information when you planned a flight there, no additional notice (such as signs or NOTAMs) was required.
If there had been changes to the airport not yet in the CS, there would be NOTAMs for the airport until the next update cycle--and you would be responsible for knowing those as well.  However, with the airport being closed five months for construction in this case, they had plenty of time to get the CS updated before it reopened.

I don’t think that the Chart Supplement for Catalina has been updated since the resurfacing because it still states that the “surface is rough with potholes and soft spots”. The repair work may have changed the slope a bit and taken out some of the hump, but I haven’t seen anything about that yet.

@JScarry, yes it is not updated in charts or supplement. I felt responsible to give heads up.


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What was the first production jet engine to use a semiconductor based control system?
What was the first operational jet engine to use a control system containing semiconductors? This would include analog systems as well as digital ones. I am assuming that analog ones came first.
This would have to be a component used for normal operation of the engine, it would not include any equipment used for maintenance or diagnostic of the engine while on the ground.
Additionally it would have to be an aviation jet engine actually installed in aircraft that flew. Not just an engine used for R & D purposes on the ground.

Out of curiosity, why do you ask?  Seems like a very specific question.

It should be interesting to learn about the difficulties they had in the development of such a system and how they overcame it. The aviation & space industries always have a low tolerance for failure, leading to interesting solutions

Your question is unclear. Are you looking for any component bolted to a jet engine or otherwise related to its operation that implemented a semiconductor (electrical generation system, for example), or only the engine control system?

Can you define what you mean by "semiconductor"? It is an incredibly broad term meaning everything from LED's to transistors and high end microprocessors. The history of semiconductors goes back into the 1800's

It seems like you are more looking for the history of semiconductors in aviation engines, which would be a book topic.

What do you mean by 'book topic' ? Are you saying this is more appropriate in the history stack exchange site?

Is there a reason to start only after semiconductor junction invention and not at electron tubes? (which where less reliable than junctions)

@mins yes, I don't have any interest in tubes. I wanted to know how semiconductors changed aviation at the time, specifically propulsion.

The RB211 as found on the L-1011 (first flight Nov 16, 1970) had a fuel control amplifier that, while it was not the primary control of the engine, was capable of controlling fuel flow.

Thanks, could you let me know where you found those documents?

Facebook L-1011 Group

The first jet engine with an digital electronic controller seems to be the Pratt & Whitney JT9D-7R4D, a 213 kN turbofan with its Digital Electronic Supervisory Control System.

JT9D engine, source: Wikipedia
From this ASME paper dated 1981:

The JT9D-7R4 Digital Electronic Supervisory Control System
  incorporates all the hydromechanical elements of previous JT9D control
  systems plus an Engine Electronic Control, an alternator to provide
  dedicated electrical power for the Engine Electronic Control, and an
  engine inlet pressure/temperature probe.

Previous engines used an electromechanical fuel controller to set and regulate thrust. For this engine the electromechanical unit was still used, but it was coupled with the electronic engine controller. If necessary the EEC could be shutdown.

Source: DocSlide
The first aircraft to be equipped were the Boeing 767-200 and Airbus A310-200, both released in 1982.

A310-221 (source)


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Can a plane with air-breathing engines in level flight achieve enough velocity to make a single orbit?
A rocket uses engines that carry both fuel and oxidizer. Most are composed of multiple stages and lift a payload to orbit. They are able to burn their engines anywhere in or out of Earth's atmosphere since they carry both fuel and oxidizer. This is necessary to achieve orbital elevation and velocity.
Can a plane with air-breathing engines achieve a high enough speed in level flight such that it reaches orbital velocity? The idea being the plane could use the fuel in its tanks and the air in the atmosphere (at whatever altitude makes the most sense) to gain enough kinetic energy that the plane could then "climb" to an orbit. This would be similar to a zoom climb, but resulting in the plane entering a stable orbit. The plane could burn its engines until flameout as it ascended through the atmosphere. At that time it'd be dependent on kinetic energy alone. The engines, fuel tanks, and other equipment for air breathing flight can be jettisoned at this point if need be.
For the purposes of this discussion, orbit is defined as a trajectory having a minimum altitude of 100 kilometers. Once at this altitude, the vehicle would need to be able to make at least trip around the Earth without requiring additional delta-v from any onboard source. If the path taken was highly eccentric or even whatever it's irrelevant to this discussion as long as the minimum altitude is maintained. There is no requirement for re-entry at a specific location or even that re-entry is survivable by the craft.
The craft could use esoteric materials, fuel sources, engines, and even construction so long as those have been used in at least one prior sub-orbital flight.
If the plane needed a Reaction Control System to control its trajectory once it reaches high altitude this would be acceptable. These systems don't have enough thrust to actually send the plane into orbit.

When the space shuttle returns from orbital velocity, it's going something like Mach 25, and the atmospheric heating issues at that speed are extreme. Building a craft that uses air-breathing engines to reach those sorts of speeds, that also deals with the incredible heating, seems like a very tall order, which might explain why it hasn't happened yet.

Also see on Space.SE: Can you get to orbital speed with an air breathing engine?

I'm voting to close this question as off-topic because it is already answered on [sx.se]

@DanHulme just because a question is answered elsewhere doesn't mean it has to be off topic.

@fooot I agree, and I don't think it's actually "off topic", but I don't like to see answers to a good question split up like this, and you can't close as duplicate of a question on another site.

I updated this to make it a much narrower question. I'm not really asking about a reusable spaceplane.

@mins can you please review this one and consider lifting the hold?

No.
Currently the altitude record for a jet is 37,650m (This is a zoom and climb record, not sustained flight).
Ralph J sum up the issue pretty well, but let me add some data:
Ramjets are the kind of engines that looks the closest to what you want to achieve. They top out at 2km/s Orbital speed would be 7km/s. And that's with a minimal payload.
There is an inextricable issue with forgoing O2:

You need significant O2 to have thrust
You cannot get thrust if there is atmosphere (Drag+heating)

Lastly; to achieve an orbit, you need a circularisation burn, that can only be done outside of the atmosphere.
The lowest point of your orbit cannot be higher than the lowest burn performed.
Using only atmospheric O2; your orbit will be bound to reenter on achieving your first revolution.
(If you intend to achieve escape velocity however, this is not an issue anymore).

Just a nit-pick: Orbital speed would be 7km/s. And that's with a minimal payload orbital speed does not depend on mass at all, it's always the same for the same orbit. A larger mass will need more fuel to reach that speed, though.

This has long been a desire of the aviation community; in fact, at the beginning of the space race the Air Force side tried to get to space using planes. That led to scores of studies on reentry vehicles and culminated in the X-15 program.
On the other side were the Army guys who got substantial help from other Army guys (on both sides of the Iron curtain). Ironically, those other Army guys first wanted to offer their rocketry to the Luftwaffe, but there it was perceived as hopelessly inefficient.
The main problem in achieving speeds in excess of Mach 4 with air breathing propulsion is to slow down the air enough so it can be heated, usually by combustion. Slowing down air will heat it up, so the trick is to slow it down only somewhat so the heating stays limited and leaves enough margin for combustion. Unfortunately, there is always some air which is slowed down to a full stop and heated to the stagnation point temperature, which rapidly exceeds the limits of known construction materials above Mach 5, so active cooling is required.
With a cryogenic fuel a lot of heat can be absorbed, and there are plans to design engines which cool themselves and the incoming air in order to reach close to orbital velocity. The last step in those plans is covered by a pure rocket, however. The switchover from air breathing to pure rocket propulsion in that case has been set at Mach 5.4 and 26 km altitude.

The SABRE 'hybrid' engine is a very interesting development: https://youtu.be/Jf3F9AQ-JI8

The craft will need to reach escape velocity of 11 km/s, over 40,000 km/h. The fastest craft with an air breathing engine, the X-43A, has flown at 10,617 km/h, so we're not there yet unfortunately.

Scramjets only work from M 4.5 onwards, so if you were to use only air creating machines you would have to start with a turbine jet, then from M 2.5 onwards a ramjet, and then a scramjet - and then you're only 25% of the way speed-wise. However, a platform built like that would be useful for bringing larger payloads into orbit than with rocket engines alone. There seems to be no escaping rocket engines in the foreseeable future though.

Yes I seem to have trouble on the ipad today, will try again with the laptop later.


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How feasible is a nuclear powered lighter-than-air vehicle that uses steam as the lifting gas?
An interesting question was asked regarding the use of steam as a lifting gas for lighter-than-air vehicles here: What are pro/cons of steam as lifting gas for airships?.
Many of the challenges with steam revolve around the large amounts of power needed to generate enough steam, along with the losses associated with the steam cooling/condensing on the envelope skin.
However, if one were to use a nuclear power source of some kind (let's suspend the safety concerns, as we're only concerned with feasibility), would there be point where a large enough vehicle could theoretically use steam as a lifting gas?
Edit:  I'm not equipped to do the sort of math required to answer the question.

Why do you think it might not be theoretically possible?  With enough engineering effort and money all sorts of wild ideas are technically feasible.  If you are asking whether a nuclear steam balloon is more financially feasible than current alternatives, then it doesn't take take a detailed cost/benefit analysis to estimate that the answer is likely a resounding no.  Don't ask someone to do the math for you...

@MichaelHall Financial considerations would be a whole separate question, I think.  I was more thinking about whether it would be completely impossible (it requires an envelope size of 100 miles or something) or merely wildly impractical.  It's almost certainly not a good idea, for dozens of very valid reasons.

Well, I think your question needs more focus then.  Given that hot steam rises we have already established in the other question that it can be used to lift something.  So, the debate becomes one of an efficient heat source to generate the steam.  (e.g. BTUs per pound of weight)  I'm guessing that a small reactor would pack more potential energy than a bank of propane tanks so I don't think fancy math is required.  Just need a little old fashioned research if is important enough for you to confirm what we suspect.

We can build nuclear satellites. We can even build nuclear planes So what makes one think we can't build nuclear.......hot air balloons?

So the Convair NB-36H, a prototype US bomber from the 1950's that was designed to eventually be nuclear-powered, carried a 1 MW air-cooled reactor with a mass of 16 Mg (16,000 kg / 35,000 lbs).  If we put the reactor from the NB-36H in an airship and use it to heat steam as the lifting gas (let's assume that the reactor has enough power to keep the steam heated), then the volume required for the lifting gas to lift the reactor alone would be 1 m^3 ÷ 6.26 N * 9.87 N/kg * 16,000 kg = 25,200 m^3.  The Hindenburg, by comparison, contained 140,000 m^3 of lifting gas.  Unfortunately the Wikipedia article for the Hindenburg doesn't give the mass of the airship minus engines, passengers, and cargo, so I can't guess at how much more mass would be required for the rest of our nuclear-powered airship, but let's assume for now that the machine would be light enough to leave the ground.
Unfortunately, there are other problems.  First, if there are humans aboard, then they will require shielding.  There is no way to make lightweight shielding; shielding inevitably requires mass.  The NB-36H had 11 tons of shielding for five crew.
But it gets worse: the airship would leave a trail of radioactive gas everywhere it went, since the reactor is air-cooled.  This might have been tolerated in the 1950s, but things are very different now.  In a crash, the reactor would break apart into highly-reactive pieces, including the uranium or plutonium fissile material.
To sum up, it may be technically feasible to design an airship that uses a nuclear reactor to heat steam as the lifting gas.  However such an airship would be ridiculously expensive, and probably not be able to carry more than a small handful of passengers or crew.  It would likely irradiate anything nearby in normal operation, it would leave a trail of radioactive gas wherever it went, and it would cause a major nuclear incident if the reactor were to malfunction, or if the airship were to crash.  Such an airship would be highly impractical.

The other answer you quoted already says that steam as a lifting gas is not feasible no matter what heat source you use. A steam lifting gas nuclear powered airship is not any more feasible because you'd be limited by the amount of water you can carry, and even small nuclear reactors are heavy.
You would get much better results by simply heating air with the reactor, as air is a better lifting gas, and you won't run out of it. Assuming a pressurized water reactor here you would heat the primary coil using your nuclear fuel, and the primary coil would heat air in a secondary loop rather than water as you would when generating power. There's a fundamental problem though, the secondary loop is pretty important in cooling the reactor, and we all know what happens when a reactor overheats. There's probably a way to overcome that through design, this unlikely to happen as nobody wants to spend billions developing a nuclear reactor that could potentially cause a disaster if it were ever to fall to the earth.

You don't need a full reactor to generate heat. Radioisotope thermoelectric generators use the decay-heat of elements that are cold enough to work without active cooling. In fact you could put an old rod into some layers of lead, and it would be reasonably hot without ever melting down or blowing up. They power some spacecraft this way.

RTGEs are far too heavy for the heat they produce to lift an airship. They create electricity in space through the heat differential between the heat of the reactor and the extreme cold of space @ZsoltSzilagyi.

I lack the skills to run the math, so you might be right. Just keep in mind that I did not propose to use the heat to generate electricity to heat the ship - rather to use the heat directly. I suspect you can get those rods in any (non-military) enrichment/activity level you wish, and as there are some which do need active cooling, some should fall into the Goldilocks zone of not needing active cooling but being hot enough to lift the ship. For those, the output/weight ratio should far surpass traditional zeppelin fuel.


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Why did the YF-23 never enter service?
The YF-23 was one of the most stealthy aircraft of all time and had a range capability of 2,000 miles (that's more than some airliners can travel) but never entered service. The F-22, has high maneuverable, and is considered to be the second option compared the to YF-23 stealth and speed. So why did the YF-23 never enter service? Image source: NASA/DFRC

Ethan, please check your sources. Neither was the YF-23 particularly maneuverable, nor did it have even close what you claim its range was.

@Federico I said one of the most maneuverable aircraft. Doesn't mean that its most maneuverable aircraft of all time.

Did anyone checked comparative fire powers ?

@Ethan - The F-22... is considered to be the second option compared the to YF-23 maneuverability. The YF-23 lost the ATF competition partly because it was less maneuverable than the YF-22. Also, no fighter nor bomber has a 27,000 mile unrefueled range.

@HephaestusAetnaean sorry typo

Are you asking why it lost the ATF competition? Or why nobody has built on the YF-23, like how the YF-17 lost the Lightweight Fighter competition, but was used as the basis for the F/A-18 Hornet?

The decision was non-technical
You can hear it from the test pilots themselves:

The rating was actually based on stop lights. Individual requirements (e.g. supercruise) could be rated red, yellow, or green. At the end of the test program, both planes rated green on all requirements. This was all Secretary of the Air Force Donald B. Rice had been given to decide. So the decision had to be made on a non-technical base.
Rice had more confidence in the project management of Lockheed (this is consistent with the Global Security quote in Schwern’s answer). He was probably strongly influenced by the fact that

the YF-22 demonstrated missile launches and the YF-23 did not (even though it had not been asked to)
there are photos of the YF-22 at 60° angle of attack even though the YF-23 “would do that exact same maneuver and stabilize at that exact same angle” (49:25).

I.e. Lockheed put a lot into showmanship.
The YF-22 was probably not more maneuverable
There was never a pilot to fly both planes, intentionally. YF-23 test pilot Paul Metz, however, switched to Lockheed after the end of the program to fly the first production F-22, so he’s probably the only person entitled to compare them at least to some degree.
In the above video he states that the YF-23 “would stand side-by-side with anything else and […] exceed the capabilities of anything else” (51:03). Here, anything else sounds like it’s pointed towards the YF-22.
Thrust vectoring had no influence on the decision

At 52:06, Jim Sandberg says exactly that and repeats that the decision was made on non-technical issues because both planes were rated green on all requirements (which would include post-stall performance).
He also mentions the YF-23’s tail surfaces being all-moving, huge (almost the size of an F-18 wing!) and driven by high-speed acuators.
While thrust vectoring improves pitch and roll performance, the YF-23’s tail surfaces also provided great yaw/roll performance.

There is no proof that the YF-23 was faster
Top speed of the YF-23 is entirely speculative:

The only declassified fact is: the YF-23 with the GE engines was faster than the YF-22 with the GE engines, but only marginally faster than the YF-22 with the P&W engines (46:10).
The test pilots say that they “never tested them to their maximum speed” (51:51).
Any estimations for top speed are still classified.
The top speed of the production F-22 is rumored to be not limited by engine thrust but rather by heating of radar-absorbing materials and force on the canopy. The YF-23’s canopy cracked multiple times during the tests (some photos at 45:28) at transonic and low supersonic speeds. It doesn’t mean anything that this would be fixed with a production F-23, since we know from declassified plans that a production F-23 would also have been substantially heavier.

There is no proof that the YF-23 was more stealthy
There is a hearsay story that a general couldn’t believe the low RCS of the YF-23 mockup. Good luck finding a reliable source.
Please consider that stealthiness is not a one-dimensional quantity. See here or here – there is no easy decision, even with exact numbers (which are classified for the YF-23).
I recommend watching the above video, the explanations are pretty clear and the knowledge is first-hand.

The YF-23 lost the Advanced Tactical Fighter program to the YF-22, however it has not been made public why. The ATF evaluation is still classified and details about the YF-23's performance are not easy to come by. They are both excellent aircraft, performed similarly, and there is much speculation why the YF-22 won.
Global Security states that...

According to the Air Force, factors in the selection for production of the F-22 were a better designed for maintainability, greater potential for future development, and slightly lower cost. Secretary of the Air Force Donald B. Rice stated that the choice was based on confidence in the ability of the Lockheed team and Pratt & Whitney to produce the aircraft and its engine at projected costs. Emphasizing the importance of the Lockheed team's management and production plans, he denied that either prototype was significantly more maneuverable or stealthy. A popular view is that the decision reflected a preference for maneuverability over stealth

A derivative of the YF-23 was proposed for the 2018 Bomber, but that idea died when the program was cancelled in 2006.

Because the YF-23 lost the Advanced Tactical Fighter program to YF-22, from which F-22 was developed.
Actually, the YF-22 had thrust vectoring and was the more agile of the two.

The YF-23 design was stealthier and faster, but the YF-22 was more agile. Thus sayeth the Wikipedia. Then again being less agile of the two is probably still pretty good, so Ethan was probably not wrong.

@VilleNiemi I think the yf-23 is the better looking jet. It wins with that also.

@Ethan I'm fairly certain the USAF did not give a poop which looked better.

@egid if they don't, why did they choose the F-35 over the F-32? :)

The Advanced Tactical Fighter (ATF) competition was different than some of the other fighter competitions.  The planes never squared off in any kind of mock combat.  The pilots who flew the YF-22 never flew the YF-23 so there was no way to directly compare the 2 in that way.  The competition focused on whether or not the planes met the requirements.  Both aircraft met the requirements so the decision is said to have come down to assessments of the ability of the competing contractors to deliver the aircraft.  Northrop was busy with the B-2 and the YF-22 was thought to be more fully developed and more ready to turn into the F-22.  Some have claimed that Lockheed made a better sales pitch.  It should be noted that the YF-23 could carry 4 AMRAAM internally while the YF-22 could carry 6, which may have factored into the Air Force decision.

That make a lot of sense, usaf might think Northrop will use their a team on b2, and use not-so-a team for f22.

Three things are correct:

Both aircraft met requirements
The decision was non-technical
It was politics, not Pentagon but Congressional.

Couple of sayings hold true inside Washington, “money makes the world go round” and “follow the money.” Need to divvy up the bounty - these are immense contracts. Congressional politics come to play; Who got the last big award and which region of the country could use the financial support?
Defense Acquisition Program Manager, WPAFB, USAF retired;
Chief Scientist, Defense contractor, retired.

Welcome to [Aviation.se]! This has the makings of a great answer. If you'll take a look at the other answers provided for this question, you'll see that we're looking for answers that have some backing to their claims. If you can point to a congressional vote, strong congressional supporters of the YF-22 (and their moneyed constituents), etc. that would make it a great answer. Also, a little formatting makes things easier to read. I altered your point to make a numbered list out of them. Your credentials (impressive) should actually go in your user profile, not as a "signature".

Right now, this post is basically innuendo with no substance. As such, I'm voting to delete it. However, I'd happily retract the delete vote & upvote the answer if some factual substance were added, as @FreeMan discusses. With that sort of improvement, the answer could be very good.

Officially both aircraft met or exceeded the government requirements set by the ATF program office, but the Lockheed jet won out in the end of the ATF program.
The reasons why are a strange combination of Pentagon politics and little showmanship on the part of Lockheed.
At the time of the ATF program, Northrop was in the doghouse with the Pentagon due to program delays and cost overruns on the B-2 Stealth Bomber program, which made ATF program managers skeptical of Northrop’s proposed program timeline and budget numbers submitted with their ATF proposal.
Midway through the ATF flyoff, the Navy inexplicably added an additional requirement to the program that they wanted to evaluate the ATF prototypes to create a naval variant as a replacement for the F-14 airplane.  This requirement was added after both ATF designs had passed CDR and parts were being cut for both aircraft.  The Navy evaluated both designs and felt the F-23 would have been unsuitable for carrier operations.
In addition, USAF commanders were not totally convinced of the merits of stealth and BVR air warfare at the time of the ATF program.  Many had been pilots who had flown in Vietnam and had to deal with the shortcomings of fighting small, maneuverable MiGs in big, powerful Phantoms with out a gun.  The experiences had led to the development of airplanes like the F-15 and F-16 with suberb dogfighting capabilities.  Leaders did not want to stray from this winning formula, particularly given just how successful it had been against modern Soviet hardware in Operation Desert Storm and were more skeptical of an aircraft which relied heavily on stealth for defense and attack.  This is not a terribly fair perception; the YF-23 was a very agile airplane, particularly in the transonic and supersonic regimes of flight.  But the Air Force was more interested in an advanced F-15 with stealth characteristics, which is what Lockheed perceived and delivered with their proposal.
Finally Lockheed laid in a little showmanship with it proposal which included sorties where their jet launched missiles, giving the fallacious impression that their design was much closer to combat ready than the Northrop proposal.

The missile launch demonstration, which is what according to old books about the program I have decided for the F-22, were ordered by the program office. This according to my sources was done to create a favourable environment for Lockheed as the YF-23 was NOT invited to launch missiles, only the YF-22. This warped the competition in Lockheed's favour and led many to believe the outcome was based on political rather than military or technological considerations. Which brings back memories of the bribery scandals around the F-104.


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Why don't cockpit windows suffer pressure leaks?
The de Havilland Comet had pressure leaks inside the square windows which resulted in 3 incidents of the aircraft breaking apart in mid-air. A cockpit window has a similar square window and should be susceptible to pressure leaks.Source:(prosim-ar.com) Here is a Boeing 737 cockpit outer view. As you can see the windows are square which makes them susceptible to pressure leaks because of their square shape like the de Havilland Comet. So why doesn't the Boeing 737 cockpit windows suffer pressure leaks? And what modern methods do engineers use to reduce pressure leaks and why aren't square windows used on airliners any more?

Because the engineers now know about the problems with square windows and design them strong enough so they don't leak. If your next question is "Why aren't cockpit windows round?", then perhaps they have requirements for visibility that precludes the use of windows with rounded corners. Also, see the windows on SpaceShipOne.

Greg is right, they do have potential issues but they are understood much better with modern designs. About rounding the corners, see your related question on why they windows aren't bigger. Interestingly, new designs like the 787 and A350 also have more rounded corners.

The questions you added in your edit should be answered here.

The windows did not suffer from pressure leaks.  The problem was fatigue stress cracking which led to structural failure.


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Why do older airplanes have the wing curved upward like a 787?
I was just wondering one day about because the 787 uses a wing flex to reduce wing tip vortex, but back in World War 2 they didn't know about wing tip vortex, so then why would it be curved upwards?

You can see in the middle picture the wing is curved upwards. I see this on a lot of commercial airplanes too like the Boeing 737

It's not curved, it's just a dihedral angle for stability.

@fooot that's about actual flex, this one is about dihedral.

@Federico It's not clear what is meant by "curved wing", and the 787 is much more notable for wing flex than dihedral.

@fooot I agree, but don't get thrown off course by the wrong assuptions behind the question: 787's wing flex is not there for reducing the wingtip vortex.

What is it there for?

@Federico Exactly, the linked question explains the reason for that, which seems to be at the basis of this question.

@Ethan the question linked in my first comment explains the reason and consequences of the wing flex.

The newest edit changed Curved wing to wing flex, so I think this can now be safely closed on @fooot's duplicate identification.

@Federico Actually doing a little research and the wing flex of the 787 reduces the strength of wing tip vortex to prove you wrong just look up wingtip device on wiki and raked wing tip is there and it acts just like a winglet

raked wingtip is not wingflex

Sorry meant rake wingtip

so you did not prove me wrong.

@Federico the raked wingtip actually reduce the vortex affect by 5.5% instead of a winglet which reduces it 3 to 4%. I know its off topic but its a fact.

and neither of those are "wing flex".

nope I really got my words confused

You are confusing 2 concepts here, dihedral and winglets. What you are showing in the picture is dihedral, which is not a curvature but an angle positive from the horizontal. This angle helps improve lateral (roll) stability in flight. This is nothing new, almost all commercial jets have dihedral. Winglets improve efficiency. A Boeing 787 has both.

The raked wingtips on the 787 aren't really winglets but they have the same function.

Yeah winglets are there to reduce wing tip vortex and the 787 has a different system than winglets to reduce wing tip vortex by having the wing curving upwards decreasing the strength of the vortex. The 787 has no winglet

The original poster is not referencing winglets in their post, or a wing rake.  They are referencing that the wings on a 787 are very flexible and bend upward noticeably during flight.  That's what he's confusing with the dihedral design.  It's flexibility v. structured angle.

I do actually @PeterKämpf as I don't agree on your interpretation of the question.


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How is thrust generated by a propeller?
I get confused sometimes because I hear different theories of how propellers generate thrust.

One is that the propeller pushes air back to provide thrust.
Another is the blades generate lift creating a high pressure behind the blade pushing the aircraft forward.

Is it just one of these true or is it both? For you guys its the same way of generating thrust, but to me its two ways thats my confusion. And why does a propeller need to generate lift if it just accelerates air backwards to provide thrust. That question is my main confusion.

I assume by "under the blade" you mean behind. In this case air is not washed forward, but backward, and Federico's answer is better understood. Move is created by pushing air opposite to the move direction, to move air (by deflection) you need the blade lift effect.

Read discussions of lift production on wings.  The arguments are exactly the same if you replace the words "back" to "down" and "forward" to "up".

Why did you ask a new question when you already have a very good answer here - https://aviation.stackexchange.com/questions/19582/how-do-the-blades-on-a-propeller-generate-thrust?lq=1

Those two statements seem to say the exact same thing to me.

You already accepted an answer on your first question, with effectively the same title. Edit or comment your first question if there is something you don't understand about it. Generating lift is equivalent to accelerating air; Newton's laws of motion.

@fooot I am confused about lift being generated to accelerate air.

It's the same thing, it changes only the point of view, see Newton's third law: for each action there is an equal and opposite reaction, i.e. to create thrust, the engine has to push air backwards. Pushing the air backwards means that the air is pushing you forward and this, in the reference system of the propeller blade, is lift.

Both the methods you are describing are the same:

The propeller pushes the air behind if you are viewing from the aircraft (or propeller).
The propeller generates lift by creating a high pressure if you are in a frame of reference out of the aircraft.

Both are equivalent and can be used to describe what is going on.

So both produce thrust.

@Ethan: Yes, in the sense that a car and an automobile are both vehicles. They're literally the same thing, just described in different words.

So wait so I thought was generated by the higher pressure under the blade pushes the aircraft forward .I am confused.

@Ethan read Newtons 3rd law.

@ethan. Lift is generated by creating higher pressure under the blade and lower pressure above. You do that by pushing air behind the blade :-) they're the same thing but described in different ways (action and result, cause and effect)

If you imagine one of the propeller blades as a wing it can help you understand. It spins around, moving air over both sides of its blade. It is producing thrust the SAME way a wing produces lift. Airflow over the top surface, which is in front of the airplane, causes lower pressure. That negative pressure sucks the airplane forward the same way negative pressure over a wing has the effect of lifting the plane.
Thinking of it this way also helps with understanding P-factor.

negative pressure over a wing has the effect of lifting the plane: True, but that's not the main source of the lift.

What do you mean by sucks the airplane.  How I think it is the blade generates lift and the high pressure behind the blade pushes the aircraft forward. Am I correct because I am really confused.

Ethan, that is the same thing. If high pressure is below and low pressure is above, the plane moves from high to low going "up". Whether you prefer to say you are pushed up or pulled up is the same thing.

When I think of fluids and pressure gradients, I go back to Newton's first and second laws. A fluid can only accelerate in the presence of a pressure gradient, and if there is a pressure gradient then there must be acceleration (ignoring gravity for the moment). So your propeller accelerating air past it only occurs because the propeller induces a pressure gradient in the air (high pressure behind the propeller, low pressure in front), or the pressure gradient occurs because the propeller accelerates the air.  They are essentially one and the same fenomenon, either side of the equation F=MA.


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Is reverse thrust needed on a long runway
Every time I have landed on a airplane reverse thrust is needed, but what if the runway is 18,000ft long. Because if the runway is longer couldn't you save fuel by not using the reverse exhaust

Please everybody stop reporting my questions as bad because if I get anymore bad question reports then I can't ask questions anymore and I absolutely love this website. Its better than google giving me answers more explained than google can give me. I am only 14 years old and I am curious about airplanes and hope to be an aerospace engineer so please do not report my questions as bad thank you.

We are not saying your questions are bad, just that they have been asked and answered before (or at least someone thinks so). The idea is that people with the same questions can find answers. You can use the search box at the top right to see if similar questions have already been asked. If there is already a question asked, then you get to learn the answers without the trouble of asking a new question.

If you have searched, or have read the "possible duplicate" link, and feel your question is different, then feel free to edit your question to clarify what your new question is asking and indicate why it's different than the one being referenced. If you look through the comments on older questions, you'll see this has happened many, many times, and is an expected behavior.

If you are interested in what methods planes use to stop, this question is also related.

I just changed my question to be more different.

I already know how reverse exhaust works I am just curious to see if you really need it on a longer runway

The first question I linked also includes when it needs to be used, and the second one talks about how useful different braking methods are.

I'm just going to keep this question up guys, but I did take down some of my recent questions.

I think most of your questions aren't too bad. The search function on this website isn't the best so it may be hard to find out if someone else already asked your question. Usually google is better, especially if you put site:aviation.stackexchange.com in the search field, restricting the search to this site.

The current wording of the question seems different than the duplicate suggested. So I'm voting to keep this one open.

@Ethan I am glad you are here and participating in the site! If your questions get closed, we still like you, but part of what makes this site so great is the high quality standard. Take it as an opportunity to edit your questions to be better, more clear, and original.

Reverse thrust is never needed.
A reverse thrust is relatively complex thing that can easily fail and for this reason when deciding whether an aircraft can land at some runway, the calculations are done without assuming reverse thrust. And of course the stopping distance for aborted take-off is also without thrust reverser, because if your engine failed, it won't provide any.
The reason to use reverse thrust is to reduce wear of the brakes and tires. The kinetic energy of the aircraft is huge and when it gets converted to heat in the brakes, they can get pretty hot. So if available, pilots always use reverse thrust to ease the brakes.
But it's not a big deal if not available. Thrust reversers are on MEL (minimum equipment list) for most if not all aircraft meaning the aircraft can be dispatched with thrust reversers inoperative. The brake wear will be higher from the more intensive braking, but it is better than having a plane wait for spare parts at some remote location.
Regarding long runways, there is almost always a possibility to turn off the runway earlier, which often saves time for the aircraft (shorter route to taxi) and makes the runway available for next aircraft sooner. So pilots usually still want to use some reasonable braking.

Don't you mean they are NOT on the MEL?

An example where you hardly feel the pilot brake, let alone use the reversers, is runway 14 at LNK.  It's 8,750ft long, the only sensible exit to the terminal is at the far end and traffic is very light. A typical passenger plane flying into there is something like a CRJ-100, which requires barely half that runway length even at MTOW.

@TomMcW Nope - it's a slightly confusing name, but it would be impractical to list every piece of equipment / nut and bolt on an aircraft so the MEL only lists pieces of equipment (With caveats as required) that aren't required.

Aircraft don't need thrust reversers on a long runway, in fact they often don't need it at all. It just helps in decelerating, reducing the wear and tear of the brakes and tires. That comes at the cost of fuel, but it saves on downtime replacing brake discs and tires.
Another reason to use the reverser is that sometimes it saves taxi time to take an earlier runway exit. This saves fuel and time = money.

Can you specify the cost saving with shorter taxiing?


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Are the Boeing 747-8 engines more efficient than the 747-400 engines?
So I was doing some research on the Boeing 747-8/4 engines. I discovered that the PW4056/62 (747-400) has a much lower bypass ratio and weighs a lot less, and it is much smaller than the GEnx-2B67 (747-8). So it really seems the PW4084 is the more efficient engine. If it is not true than what improvements have been made on the  GEnx-2B67 to make it the more efficient engine? GEnx-2B67 engines
PW4056/62 engines

Related: What prevent jet engines design with bigger by-pass ratio?

Efficiency, of any machine for any purpose, means the ratio of useful work done to energy used (which for engine means fuel burnt). Weight or size of the engine has nothing to do with it.

In most of the engine performance parameters, the GE GEnx-2B67 is a better and more efficient engine compared to the Pratt & Whitney 4084. There are multiple reasons for this.

Fuel Consumption: This is the parameter of the engine airlines are most interested in, as it affects their bottom lines. The Thrust Specific fuel consumption gives the fuel consumed by the engine for unit thrust produced. In this case, the GEnx has over 20% improvement over the PW 4000 series (0.27 versus 0.348).
Bypass Ratio: In general, a higher bypass ratio means a more efficient engine. The GEnx has a much better bypass ratio compared to the PW 4084 (8.6:1 versus 5.3:1).
Engine Noise: The GEnx engines are specifically designed for reduced noise levels, incorporating the Chevrons.
Thrust to Weight Ratio: This is a much better parameter compared to the weight alone for engine performance as the weight increases due to larger bypass fans, for example. In this case, both the engines have almost the same values (5.5 and 6).
Thrust: Higher thrust means improved aircraft performance. The PW 4062 produces a maximum of 62,000lb thrust while the GEnx produces over 67,000 lbs of thrust.
ETOPS: Another advantage of GEnx engine is that it is certified for Extended-range Twin-engine Operational Performance Standards (ETOPS), (in Boeing 747-8) which indicates that the reliability of engine is high. The PW 4062 engines used in 747-400 does not have this certification (Engine is only a part, albeit important of ETOPS certification though)

The engine used in the 747-400 is the PW 4056 and 4062. PW 4084 is used exclusively in Boeing 777.

Yes. According to GE, the GEnx-2B consumes 15% less fuel than the CF6, which was contemporary to the PW4084 on the 747-400.
The bypass ratio of a jet engine makes it more efficient, not less. A higher bypass ratio provides more thrust from the fan air, which means the core section can use less air and therefore less fuel to provide less thrust. This increase in efficiency is the reason turbojets evolved into turbofans and have been increasing in bypass ratio as technology improves.
One consequence of a higher bypass ratio means the engine does get larger and heavier. However, the increase in efficiency is more than enough to offset these costs.
Besides increasing the bypass ratio, there have been many internal improvements in the GEnx line of engines, discussed in the GE link above. These changes include composite fan blades and fan case, which can be lighter than the metal alternatives. Throughout the engine there are also aerodynamic improvements to increase the efficiency of air flow through the engine, as well as more new materials and manufacturing technology.


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How does ignited gas spin the turbine?
For the N1 fan and N2 compressor to move, the turbine needs to spin in an airliners engine. How does energy from the ignited gas spin this turbine? Do the blades on the turbine generate lift just like a wing and spin to spin the N1 fan and N2 compressor?

Find a pinwheel, and blow on it, the same way that rapidly expanding gas would move.  Watch the pinwheel spin.

Maybe it's not important to the question, but I have a feeling that the picture shows a zero bypass ratio engine, thus it does not have N1 and N2.

I am asking about the exact process of how this spinning motion happens.

@SteliosAdamantidis True I just wanted to find a picture with a turbine. This is the only good one I could find.

In the shortest possible answer, yes.  The blades are like any other aerofoil.

The picture shows a pretty unusual engine, if such thing even exists: a radial flow geared turbofan. Many early turbojets were radial flow, but they had no fan, not to mention geared. While modern turbofans are axial flow, with gears only slowing coming in fashion.

I will attempt to answer the question though I'm not an engineer. Each spool (N1, N2 etc) has a compressor in the front and a turbine in the rear. Compressor is a set of rotor blades followed by stator vanes. This is a compression stage. Turbine has the opposite setup: stator vanes followed by rotor blades. They are either pure impulse turbines or impulse/reaction turbines. You may have a look in wikipedia to see the turbine working principle.
Now the high speed combusted air that comes out of the combustion chambers put the turbine in motion. The turbine moves the shaft, the shaft moves the compressor, the compressor feeds the combustion chamber with compressed air and that cycle goes on and on for as long as there is fuel going in the chambers.
Here is a diagram of how is the turbine "set to motion". Red arrows show how the airflow is guided from the nozzles to an impulsive turbine blades.

Image source: own work
The stator vanes are convergent and the air coming through the resulting nozzles is accelerated. As the accelerated air impacts the curved rotor blades, they cause aerodynamic forces on them, similar to those caused on a wing (as others already said). These forces set the turbine to motion.
EDIT: Added image and corrected compressor and turbine stages description

Slight addition from an engineer: you describe an impulse turbine, which converts pressure into momentum through a nozzle, and momentum into work. The other end of the spectrum is a reaction turbine, which converts pressure directly into work. In reality, jet turbines are a (computer-optimized) combination of the two.

@sanchises Sorry but I don't think I follow. I describe an impulse turbine but I mentioned the impulse/reaction turbine. The former was easier to draw. :) If I had something wrong or missing, let me know so I correct it.

Sorry, I glanced over that. Perhaps you could add 'These forces, as well as some pressure differential across the blades, set the turbine to motion'. But I guess it's not really necessary given your first remark.

A turbine is a machine that extracts energy from a moving fluid and converts it into work. In the turbine blades, the air is expanded, which produces work. In many ways, the turbines are the opposite of compressors.

"Two stage reaction turbine" by S.M.Yahya - Turbomachinery. Licensed under Public Domain via Commons.
The turbines used in the aircrafts are axial flow turbines, which employ multiple stages to extract work from the air coming out of combustion chamber.
The turbines have two parts- the stationary nozzles (or stators) and  the moving rotors. The purpose of the nozzles is to turn the incoming flow so that that it impinges on the rotors at the correct angle, while the actual work is extracted out from fluid by the rotors.

"Velocity triangle for an axial turbine stage" by S.M.Yahya - Turbomachinery. Licensed under Public Domain via Commons.
Basically, the rotors are 'turned' by the incoming fluid as shown above which produces work to rotate the shaft (which runs the compressor). In case of turbojet engines (and to some extent turbofan), the air pressure decreases, while the velocity increases. This provides the required thrust.
The main mechanism by which the turbine blades spin is that the flow turns the rotor blades by hitting them, rather than any lift being produced.

So it hits the blades to turn them. The blades don't generate any lift to turn.

In general, the term 'lift generation' is not used to describe the method by which the turbine blades turn. Similar pressure forces are involved, but the method is not like the case of wind turbines, where the blades are rotated by the lift.

So different pressures are created spinning. Not the same as lift though. Pressure develops in a different way is what I am getting out of it.

@Ethan: The blades do indeed generate lift. The definition of lift is merely a force vector generated by having difference in pressure between two sides of an object. If the blades spin, they generate lift. If they don't generate lift then they don't spin. Now, there are many mechanisms that generate lift so turbine rotors may not necessarily generate lift the same way as windmill rotors.

@Ethan It is not the gas "hitting" the turbine blades.  The blades generate a force like any other aerofoil and that force turns the turbine.  People are hesitating when you say "lift" because this has a specific meaning which is the force generated to oppose gravity.  In this case, it is not "lift" but is exactly the same mechanism of force generation.

This answer misses some small details. First, nozzles don't only control the angle of the airflow; their primary goal is to convert pressure into momentum (kinetic energy), which the vanes then convert into work. Secondly, the blades also converts some pressure directly into work; it's not just 'air hitting the blades'.


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How does a circulation control helicopter work
This essay describes that this helicopter uses circulation control of the rotor for cyclic and collective control, but not how circulation control works.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810017584.pdf

A quick scan of the linked document suggests that they're referring to controlling the relative amount of engine exhaust directed into each rotor, which (due to the downward direction of the exhaust jet that drives the rotor) controls how much downward deflection each blade gives its airflow.  By making this differ from one blade to the other, the rotor can be tilted without twisting the blades at the root as would usually be the case with large, heavy lift rotor designs (the effect is somewhat like the Bell-Hiller paddle system often seen on small helicopters).
The resultant rotor tilt gives pitch and roll control, which are used (directly, or by mixing rudder effect) to move forward, aft, or sidewise in hover, and to control speed and climb/dive, plus turn, when in forward flight.


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How to apply the TO/GA time and EGT limits?
If there is a published 1) EGT limit and a 2) TO/GA time limit, which one should be applied when the EGT is well below the EGT limit and possibly even below the 'max continuous' EGT. Particularly with consideration of terrain avoidance procedures that require climbing to a high altitude (10,000 ft) for terrain avoidance.

Is this part of a normal flight plan or an abnormal maneuver for an emergency? Other than that, this sounds like a question best served by a phone call to the engine manufacturer.

The TO/GA time limit and the EGT limit are hard limits mandated by the approved flight manual. They must be adhered to independently and cannot be traded off between the two.
Takeoff performance is calculated so that if a safe altitude above terrain and obstacles cannot be reached within the time limit, aircraft mass must be reduced rather than the TO/GA time increased.
Having said that, if things don’t go as planned during takeoff e.g. for reasons not known beforehand, I‘d recommend to bust the time limit rather than fly into the side of a mountain, if the choice is only between the two...

"I‘d recommend to bust the time limit rather than fly into the side of a mountain" - that seems like a rather practical recommendation. Rebuilding an engine or two should be cheaper than replacing the whole airframe and paying for the funerals...

The term may also be ITT limit (Inter Turbine Temperature).
On most engines there is usually a 2 minute to 5 minute limit on EGT/ITT and N1 (fan rpm) for both Take-off/Go Around power, and APR (Automatic Performance Reserve) power (the balls-to-the-wall thrust setting the engine automatically goes to when the other engine quits).
On most FADEC engines, the most forward thrust lever position will take you into APR for both engines and the FADEC will manage things at those limits for you, so you know you can slam the thrust levers full forward without burning up the engines in an avoidance emergency.  Same for TOGA.  You just have to observe the time limits.
On an older non-FADEC engine, you have to observe the limits and stay within them manually with the thrust levers.  On a go around for example, the pilot flying will press the TOGA button, move the thrust levers up to TOGA thrust more or less, and call "set thrust", whereupon the pilot not flying fine tunes the thrust levers to the TOGA setting bugs indicated on the N1 gauges, also monitoring to keep the ITT limits from being exceeded.
However, on a Holy Crap Emergency like a cliff in your face, on a non-FADEC engine, where it's balls to the wall or die, you accept you're probably going overspeed and overtemp, and maybe wreck the engines.  Too bad for them.
In any case, 2 to 5 minutes is plenty.  The most likely case where you would even have the engines maxed out for any substantial period that eats into a 2 minute limit significantly would be a windshear escape, but even that might burn up a minute at most (that would require a downburst 2 miles across).
The margin between maximum ITT and the ITT seen during TOGA setting is the main (but not only) indicator of engine health and life span.  An engine will have a minimum margin, and as it wears out the ITT margin gets slimmer and slimmer until you're at the limit and off it comes.

There may be a nomenclature difference between manufacturers.  On GE/CFM turbofan engines, "EGT" refers to the exhaust temperature of the high pressure turbine, i.e. synonymous with your "IIT" .

Interesting thanks.  I'll revise my post.

If you are below the EGT Limit, as you specify, then you don't need to worry about this. Then all you need to worry about is any TO/GA Time Limit, assuming you can find out what that is.


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FIS-B lookahead for SUA Status
While reading over the recent FDC NOTAMs, I saw this interesting entry come up:
!FDC 0/6362 ZOA AIRSPACE SPECIAL NOTICE..THE FLT INFO SERVICES BCST
(FIS-B) SERVICE FOR OAKLAND /ZOA/ ARTCC AIRSPACE IS REDUCING ITS FIS-B
PRODUCT LOOKAHEAD RANGE TO 5NM FOR THE SPECIAL USE AIRSPACE (SUA
STATUS) PRODUCT. SUA STATUS INFO CONTINUES TO BE PROVIDED VIA THE
FIS-B NOTAM PRODUCT. ALL FIS-B PRODUCT FORMATS REMAIN UNCHANGED. THIS
UPDATE WILL OCCUR BTN 1400-1600 ON JUNE 11 2020. ANY OBSERVED ISSUES
SHOULD BE REPORTED VIA EMAIL TO [REDACTED] 2006111400-2008111600

Am I understanding this correctly to mean that SUA status sent over FIS-B will only cover a 5nm "hockey puck" around the aircraft?
That seems incredibly small, to the point where the data seems useless now — you'd have to be practically on top of a piece of special-use airspace before you'd get any information about it.
Does anyone the background behind this change is and what the actual impact is?


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How did this Boeing 787 perform this near vertical takeoff?
At angles of attack like this an airliner would stall very easily. The 787 wing would stall at an angle of 30 degrees. The plane would have been flying at speeds of around 200mph(more likely less) at this angle and speed the aircraft would be very susceptible to stalling? How is this even possible to perform this without stalling? Source:youtube The a380 also performed this near vertical takeoff.Source:Youtube

Please take a few minutes and search for your title before you crack open a duplicate question! :)

@mins Yes you find many mountains topping 8,000 meters in the Himalayas mountain range.

@Airsick This takeoff actually happened and was on the news to prove to you that's it not fake. And actually parts of Earth are flat, so your points don't have any good reasoning towards them.

@Airsick I thought it was near vertical I guess it was an illusion created by the camera.

You need to understand the difference between angle of attack and pitch angle.  There is no way for you to know the AoA by looking at the photo.  In essence, you would also need to know the speed and flight path.

Perhaps you might want to read up on telephotography. Perspective in these images is severely distorted. For example, the Boeing's left wing looks tiny compared to the right wing. All in all, a 30° angle would be a very generous estimate in my opinion... Oddly related

First of all, it was nowhere near vertical. It is basically an optical illusion created by the camera angle.
Second, and most importantly, what you are seeing is the pitch angle and not angle of attack.
As it can be readily seen from the following image, the angle of attack and pitch angle can be significantly different.

Image from What is Angle of Attack? by Boeing
Angle of attack (AOA) is the angle between the oncoming air or relative wind and a reference line (usually fuselage centerline or longitudinal axis in commercial aircraft) on the airplane or wing.
Pitch angle (attitude) is the angle between the longitudinal axis (where the airplane is pointed) and the horizon.
Flight path angle is the angle between the flight path vector (where the airplane is going) and the local atmosphere. In other words, it is the angle
between the flight path vector and the horizon, as far as a commercial airliner is concerned.
When referenced to the atmosphere, the angle of attack (AOA) is the difference between pitch angle and flight path angle. Depending on the aircraft atitude, they can be very different. During climb, usually the pitch is increased at constant angle of attack.
For example, in a steep descent, an aircraft could reach very high angle of attack if the nose is below horizon. While flying upside down (not something that happens in an airliner, I might add) , both differ by around 180 $^{\circ}$.
So, the angle of attack in this takeoff is surely well below the stalling angle of 787.

@mins You're right. Corrected the mistake. Actually, that is the pitch angle. The irony though.

One other thing to note is that any aircraft can flu vertically - assuming it is travelling fast enough forwards, it can then pull up, it won't sustain that speed for long, trading momentum for altitude, it wouldn't be a normal takeoff, but it could look like one. This technique is used regularly at air shows

The plane is likely extremely lightly loaded, and it is not flying at 30 degrees AoA. The angle the plane is making with the ground is very high, but the angle it makes with the freestream (i.e. the AoA) is probably still quite small (10-15 degrees at most, I'd expect).


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Why are speed restrictions imposed for flights flying below 10,000 ft?
I know that restrictions do not always apply and ATC can cancel them or pilots can request for speed restriction being canceled. But why is there such a speed restriction in first place? Are there any reasons other than noise abatement?

Because in the areas were aircraft need to operate below 10;000 ft, the density of traffic is higher.

The speed limits were set by FAA in the early days of jet age for better control of the aircraft and safety where the air traffic (in VFR) is the densest and have little to do with noise.
FAR § 91.117 states

Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 m.p.h.).

TWA Flight 553, a DC 9 collided with a Beechcraft Baron, killing 26 people on March 9, 1967. NTSB investigation determined that due to the high rate of descent of the DC-9, its pilots were not able to see the other plane in time to avoid a collision.
Following this accident the FAA issued Advisory Circular 90-32 titled 'Air traffic control and general operations, radar capabilities and limitations' in Aug 1967.
According to NTSB report on the accident,

The FAA has adopted a rule establishing that all aircraft flying below 10,000ft m.s.l will be limited to a maximum speed of 250kts effective December 15, 1967... (to) provide a more realistic 'see and avoid' environment in the airspace below 10,000 feet mean sea level (MSL) where the traffic congestion is greatest ....

This is the correct answer, but lower speeds below 10,000 are also advisable for other reasons, such as that being where pesky birds like to hang out and bird encounters at 400 knots can be quite unpleasant.

There is also a lower limit of 200 Kts in VFR corridors through Class B airspace.

Nice. I would be interested though in any details regarding European airspaces. Did they just use the knowledge from that accident in USA and followed FAA's example? Or they performed their own research?